Campaigner Richard Emery claims a loophole in Santander's system was exploited by fraudsters to direct people into transferring money. Santander refutes any claim of a loophole.

The PSR's initial findings following the Which? super-complaint stopped short of recommending automatic compensation for victims of fraud.

However, it did say that banks should be doing more to combat this type of fraud.

Specifically, this included a demand for a common approach from banks in tackling fraud and the collection of more data on the issue.

The PSR's full report into the issue is not expected until late August or early September.

Action plan

Which? said that, in the meantime, there was not enough evidence of banks taking "meaningful action".

In a new letter to banks, it is demanding that they outline what has been done so far.

Gareth Shaw, money expert at Which?, said: "Despite the fact that consumers are still losing life-changing sums of money to fraudsters, it is not clear what meaningful action the banks have taken to protect their customers.

"People assume that banks will look after them and their money. So it is vital that the industry, regulator and next government act quickly and decisively to tackle financial fraud. Failure to do so will continue to leave consumers paying the price."

But a spokesman for Financial Fraud Action UK, which coordinates the banks' anti-fraud strategy, said: "We have agreed a clear action plan with the regulator on push payment fraud and the industry is working hard to deliver this to the agreed timetable.

"The PSR has already stated it will review progress in the second half of 2017.

"Across the industry, and with partners, we are developing new processes to help police intervene when potential victims visit a bank branch, and we are exploring new ways to track stolen funds moved between multiple bank accounts. We are also running our largest ever fraud awareness campaign."

How to protect yourself against "push" fraud

When you transfer money from your bank account, you are asked to enter three pieces of information: the name of the payee, their account number, and the sort code. However, only the last two are cross-checked by the bank. So putting in the correct name is no guarantee that person will get the money.

Financial Fraud Action UK offers the following advice:

Never disclose security details, such as your PIN or full banking password